1. Field of the Invention
The present invention relates to an analog multiplier circuit, and more specifically to a high precision four quadrant analog multiplier circuit of a so-called floating input type, which can be effectively used particularly for modulation and demodulation of an analog signal.
2. Description of Related Art
Known conventional analog multiplier circuits include a Gilbert multiplier circuit composed of only bipolar transistors, a MOS multiplier circuit formed by substituting MOS transistors for the bipolar transistors of the Gilbert multiplier circuit, and a CMOS multiplier circuit formed by constituting the Gilbert multiplier circuit by CMOS transistor circuits.
In the Gilbert multiplier circuit, when the magnitude of each of two input signal voltages V.sub.1 and V.sub.2 is extremely smaller than 2 V.sub.T (where V.sub.T =kT/q, K: Boltzmann's constant, T: absolute temperature, q: electric charge of unit electron), an output current is substantially in proportion to V.sub.1 .multidot.V.sub.2. Namely, when each of the input signals is a small signal, the Gilbert circuit functions as the multiplier. In addition, each of the input signals must be applied in the formed of a differential signal
Similarly, the MOS multiplier circuit functions as a multiplier when a pair of input signals are small. In addition, this MOS multiplier circuit is disadvantageous in that a linear operation range for one of the input signals is smaller than that for the other input signal. Furthermore, the CMOS multiplier circuit also has only a narrow input signal range which can ensure a good linear operation. In each of the MOS multiplier circuit and the CMOS multiplier circuit, furthermore, each of the input signals must also be applied in the form of a differential signal.
As mentioned above, the conventional multiplier circuits have been disadvantageous in that the dynamic range is narrow and each input signals must also be applied in the formed of a differential signal.